Sulphuric acid treatment of oils



T. o. EDWARDS JR.. ET AL 2,155,007

SULRHURIC ACID TREATMENT OF OILS Filed Aug. 17, 1936 3 Sheets-Sheet 2 (iW? A7'7.'ORNEK April 18, 1939.

April 18, 1939.

PERCENT JULFU/Q "i'. o. EDWARDS. JR.. ET AL 2,155,007

F'iled Aug. 17, 1936 Patented Apr. 18, 1939 UNITED STATES 2,155.00:smrnmno ACID mamn'r or ons Thomas Oliver Edwards, Jr., Associated, andDavid Dewey Stark, Watson, GaliL, assignors, by mesne assignments, toTide Water Associated Oil Company, San Francisco, Caii1., a corporationof Delaware Application August 17, 1936, Serial No. 96,408

6 Claim.

This invention relates to improvements in treating hydrocarbon oils forthe removal of sulphur and other undesirable constituents, such as thosewhich are gum forming and those which causecolor instability, and isparticularly adapted to the treatment of petroleum and its distillates,especially the gasoline fractions derived from cracked petroleum, withsulphuric acid.

The generic form of the invention has been 10 disclosed and claimed inour co-pending application, Serial No. 532,000, flied April22, 1931, nowPatent 2,052,852, and the present invention is a continuation-in-part ofsaid application.

The removal of sulphur from petroleum to a 16 commercially feasible lowfigure by the use of sulphuric acid has heretofore presented manydiillculties broadly solved in our said co-pending application, but thepresent invention comprehends improvements in the mode of operation 20providing for sulphur removal to a still lower flgure coupled withdecreased losses .of valuable hydrocarbons.

This is accomplished by the selective polymerization of the sulphurbearing compounds in pctroleum or its distillates effected by theapplication of sulphuric acid to the petroleum under controlledtemperature conditions during a predetermined period of contact. Undersaid controlled temperature conditions sludges of improved fluidity areproduced and the oxidizing action of the sulphuric acid with subsequentgeneration of large volumes of S02 is minimized, thus preventingincreased and uncontrolled velocities throughout the system.

It should be emphasized that the herein described removal of undesiredsulphur compounds from the petroleum selected for treatment is eilectedby selective sulphonation and polymerization, the latter feature beingof major importance. In so operating, the polymerization andsulphonation oi. desired non-sulphur bearing unsaturated hydrocarbons isminimized and, in consequence, the total yield is appreciably increased.

The contacting of sulphuric acid, or acid sludge,

with a designated oil, such as cracked gasoline,

for the removal of sulphur compounds is preferably best accomplished ina true countercurrent flow system, such as described in our aforesaid oco-pending application, and suitable apparatus embodying a mode ofoperation is shown in the accompanying diagrammatic sheet of drawings.

Referring to Fig. 1, a selected petroleum oil, such as cracked gasolineor pressure distillate 55 which may or maynot have been previouslytreated in known ways for the removal of impurities, is supplied fromstorage Hi to a pump H which forces a predeterminedstream of the oil ata certain velocity through a cooler l2 into the lower portion ofa'treating tower I3.

The tower l3 may be one of a'series or similar towers filled withsuitable contact material it to a degree suiiicient to assure effectivecontact of the oil with the sulphuric acid, or acid sludge, used and thecapacity of tower i3 may be such 5 that the entire contacting may takenplace in one large tower, or a similar capacity may be acquired by aplurality of towers in series, as later described. Due to constructionquestions in which economyis a factor, the use'of a series of towers ispreferred.

The contact material It used in tower l3 may comprise Raschig rings ofpredetermined size,such as 1 in. diameter, to provide efllcientcontacting of oil and acid compatible with a predetermined l5 flow rateand such contact rings may be supported in the usual fashion on aperforated screen or plate Ila. Other suitable contact material may beused, such as sized gravel, crushed rock,

glass beads, and the like, all such material being 20 preferably wettedby the acii rather than by the oil.

As illustrative of a single tower mode of operation, the acid or acidsludge is supplied to a pump l6 which connects with spray l5 and theacid sludge is dispersed in line particles by pump it in the presence ofa relatively large volume of the oil taken after treatment and returnedto the treating tower for such dispersal purposes and for the purpose oftemperature control.

The mixture of oil and acid sludge is conveyed through spray [5 to theupper part of tower l2, wherein the velocity of the combined stream isreduced to permit separation of the acid sludge particles and depositionon the contact material 35 H to descend by gravity in countercurrentflow through tower l3 against the uprising oil.

The normal flow of oil from cooler l2 through tower I3 is taken offthrough line i1 and is augmented in volume by the 'oil passed throughspray 40 I 5 with the acid sludge from pump l8. In its passage tosettling tower I! the oil is cooled by means 01' a cooler I! to thedesired temperature. A relatively large volume of this precooled oil issupplied through line 22, controlled by valve 2| into the suction ofpump it, wherein it is mixed with fresh acid and enters the precedingtower i2 through spray IS; the remaining portion of the oilapproximately equal to the raw oil charged by pump it passes upwardthrough tower I8 leaving through line 22 controlled by a pressureregulating valve 23. Settling tower It may be of the same constructionand have the same filling as tower i3.

In the special case of single tower operation on highly unsaturatedpressure distillate, or

cracked distillate, such as vapor phase gasoline, the reactivity ofstrong acid is too great and results in excessive treating losses. Undersuch conditions the chemical reactivity may be modified by admixturewithin the system with acid sludge. Under such a mode of operation asludge level L-L is maintained below the gasoline inlet in tower l3 andthe sludge formed inwhole or in part passed through lines24 and 25, therate being controlled by valve 23, and mixed with fresh acid from supplytank 21, the rate of supply of the fresh acid being controlled by valve28, and the mixture is then injected into the suction of pump l3accompanied by relatively :large volumes of precooled oil passed throughline 28 and control valve 2|, through spray |5 to the upper part oftower |3. Excess sludge formed and not desired for use may be withdrawnthrough valve 23 to sludge tank 38.

The preferred mode of operation utilizing multiple treating towers inseries is shown in Fig. 2. The system diagrammatically illustratingthree acid treating towers 3|, 32, and 33, and one settling tower 34,may be composed of two or more acid treating towers. a

The three acid towers 3|, 32, and 33 may be identical in constructionand operation, being partially filled with suitable contact materialsuitably supported as described under single tower operation on screens3|a. The settling tower 34 is likewise partially filled with contactmaterial acting as a coagulating medium to collect any acid sludgematerial which may be carried by the treated gasoline. This sludgesettles downward and may be transferred through line 35, valve 33, to apump 31 which passes the sludge back to tower 33 through a spray 38together with a relatively large volume of oil and a predeterminedamount of fresh acid supplied from tank 38 and line 43, through valve4|, as previously described.

The system is essentially countercurrent in that raw oil is transferredfrom storage 42 by pump 43 through cooler 44 to one end of the systemwhile fresh acid is injected into the suction of circulating pump 31under conditions of high oil circulation rates and the mixture entersthe acid surface contacting towers through spray 38. The oil passesprogressively into the bottom of each of the towers and out the top,whereas the acid sludge is pumped backward in the opposite direction bymeans of the circulating pumps 31, 45, and 43 between the towers. Theoil and treating medium thus flow countercurrent toeach other.

To describe the exact flow, raw oil from pump 43 is precooled to thedesired treating temperature by means of cooler 44 and enters near thebase of tower 3| wherein it flows upward through contact material 41,countercurrent to acid sludge which has been delivered to tower 3| bypump 43 in admixture with a relatively large volume of precooled oilfrom the bottom of the succeeding tower 32. The acid sludge is settledover the top of contact material 41 by spray 43 in a finely dispersedstate in the above mentioned circulated oil. The oil charge augmented bythis circulated oil passes through line 43 to the lower part of tower32, being cooled in passage by cooler 53.

From the free space at the base of tower 32, a portion of the oil iswithdrawn with acid sludge which has been coagulated and settled bygravity in tower 32 through line 5| and is then circulated by means ofpump 43 back to the top of tower 3|, the volume being controlled byvalve 52. The remaining oil, roughly approximately equivalent in volumeto the once treated charge, passes upward countercurrent to acid sludgeof increasing reactivity, which has been supplied to the top of tower 32through spray 53 by means of pump 45 with a high ratio of precooled oilfrom the succeeding tower 33. The oil, augmented as in the precedingtower 3| by the circulated oil, leaves tower 32 through line 54 beingcooled by cooler 55 before entry into tower 33.

The oil in the free space at the base of tower 33, as in the precedingcases, is divided into two portions, one of which may be circulated inorder to control a high ratio of oil to acid sludge through line 53controlled by valve 51 and pump 45 to tower 32. The partially treatedoil from the top of tower 32 is passed upward countercurrent to acidsludge in tower 33 and meets fresh acid which has been supplied to thetop of tower 33 throughv spray 33 in admixture with large ratios ofprecooled oil circulating from settling tower 34 through line and pump31 to-tower 33. The fresh acid from tank 38 is supplied through controlvalve 4| and line to thesuction of said circulating pump 31. v

The stream of oil, on reaching the top of tower 33, is augmented asdescribed with circulated oil from the succeeding tower and leavesthrough line 58 to settling tower 34 being precooled in cooler 53. As inthe preceding tower, a portion is circulated back and in this way theoil charge which has been acid treated in three towers passes upwardthrough contact material which in this case acts as a coagulating mediumto separate finely divided sludge which may be carried with the oil.This coagulated sludge settles to the bottom of tower 34 and istransferred with the circulating gasoline through line 35 and pump 31 tothe top of tower 33.

The acid treated oil leaves tower 34 by means of line 38 and controlvalve 3| and is then subjected to the usual finishing processes as waterwashing, and caustic neutralization, the mechanics of which are commoninthe art. Acid treated oil in the single tower operation (refer toFig. 1) leaving settling tower l8 through line 22 is also subjected tothe above mentioned finishing procedure before the rerunningdistillation operation for the removal of polymerized compounds.

As in the special case mentioned under single tower operation, in whichit may be advantageous to mix the fresh acid with acid sludge, the samemay be accomplished in multiple tower operations in the followingmanner:

Sluge levels X-X, Y-Y, and Z-Z may be permitted to form in the lowerpart of towers 3|, 32, and 33 respectively and line 32 permits thewithdrawal of sludge from tower 3| to be passed to a header 33,controlled by valves 34 and 35, for distribution as desired to any orall of the circulating pumps 31, 45, and 43 for use in the-describedmanner.

For closer control of regulated ratios of oil to acid sludge, valvecontrolled lines 33 and 31 may lead from above and below the sludgelevel Y--Y in tower 32 to the suction side of pump 43 and likewise valvecontrolled lines 38 and 38 may lead from above and below the sludgelevel Z-Z in tower 33 to the suction side of pump 45, in the event thatthe total sludge is not desired to be withdrawn through linesv 5| and 53from towers 32 and 33 respectively.

Crossovers 10 and 1| are provided to pass sludge from tower 3| to eithertower 32 or 33 or both and crossovers 12 and 13 are provided to passsludge back to pump 31, or valve 14 may be closed to pass unrequiredsludge back to sludge tank 15. Likewise by manipulating valves 13, 34-,

iii)

and 85 and the other described valves, sludge 'may be passed from anyand all of the towers 3|,

32 and 33 to sludge tank 15.

The arrangement of lines and valves described is such as to assure themaximum utilization of the acid sludge in the system in order to effectthe highest degree of selective polymerization without unduesulphonation and at the same time to provide for continuouscountercurrent contacting and temperature control.

To this end, it is obvious that acid sludge may be passed from one towerto another as efficiency may require.

With the above described flows, a preferred selective sulphonation andpolymerization of sulphur compounds without excessive sulphonation andpolymerization of non-sulphur bearing unsaturated hydrocarbons may beefiected either in a single tower of somewhat'excessive height, orpreferably in multiple towers, by contacting the acid and acid sludge,in true ,countercurrent flow with the oil to give a predetermined timeof contact by the use of proper contact material under controlledtemperature conditions.

Temperature control is important, first, to

allow the selective polymerization action of the sulphuric acid and acidsludge on the undesirable constituents such as sulphur compounds,second, to maintain a desired fluidity of the acid sludge to allow theeffective utilization of the acid values thereof, and, third, to preventexcessive oxidizing action of the acidand the resultant production oflarge volumes of S02, the latter having a deterrent effect in increasingvelocities throughout the system which thus may disturb the desiredequilibrium in operation.

If it be assumed that a single tower is to be used, refer to Fig. 1. Theoil is cooled on passing through cooler I! to a desired temperaturebetween 0".F. and 70 F., preferably to a temperature of about 20 to 40F., and is then introduced into the lower part of tower I! to flowupwardly through the contact material M therein.

The superficial velocity of the oil upward through said contact materialmay be increased to a rate just insumcient to prevent the passagedownward by gravity of the agglomerated sludge originally dispersed inthe oil by means of pump "and spray l5 over the top of said contactmaterial. By superficial velocity is meant the velocity of the oilthrough tower ii if it contained no contact material. As illustrative oftreating various types of oils, superficial linear velocities of 10 feetper minute or higher have been used, but for optimum results velocitiesof 0.8 to 1.3 linear feet per minute are preferably used.

In the treatment of pressure distillate superflcial velocities of 0.1 orless up to 1 linear foot per minute are preferred.

In general, the superficial linear velocities employed in the system mayrange from 0.1 of a foot or less, up to 10 feet or more, per minute.

' The sulphuric acid used in treatment is of a. concentration from aboutacid up to and including fuming acid, preferably from about 93% acid to98% acid, and is supplied through valve 28 and line 28a to pump ittogether witha portion of the treated oil from tower it.

when fresh acid is supplied by pump I to tower I! it is distributed inthe form of a highly reactive and finely dispersed sludge over thesurface cf the contact material to descend by gravity therethrough inthe form of an extended film covering each particle of contact materialwherein the oil flowing upwardly countercurrent to the descending acidsludge is thoroughly contacted with said sludge in increased reactivityunder such conditions that maximum removal of sulphur compounds isassured by selective sulphonation and polymerization thereof.

Optimum contact conditions to this end are assured in such contact towerby the provision of an infinite number of contact steps of the oil withthe acid down through the tower, in each step the less treated oilcoming in contact with more and more reactive acid sludge;

Additionally, in accordance with selected velocities, a prolonged periodof contacting is assured so that within such period the maximum desiredpolymerization of sulphur compounds will take place. Also a controlledtemperature gradient down through the tower is established to preventexcessive sulphonation and polymerization of unsaturated hydrocarbonsdesired in the finished motor fuel while removing sulphur compoundsandother impurities such as gum forming and color unstable constituents.

Temperature control is established in two ways; first, by the initialcooling of the oil in cooler i2 and subsequently by cooler l0, and,

second, by passage of high ratios of cooled oil with the sludge-throughthe pumps circulating oil and sludge back from a succeeding tower to apreceding tower.

In single tower operation when processing a pressure distillate producedfrom California residuums of the following characteristics:

A. P. I. gravity at- 60 F 59.0

Sulphur "percent" 0.70 l' nsaturatiom do. 22.0 Englerz.

1B1 90 30 1Q 310 E1 MB 5 117 40 234 so 340 Room. 91.0 10 131 50 204 00370 Res. 1.0 20 104 200 05 300 Loss 1.0

and when such is cooled to an entry temperature of 40 F. and passed intotower I! at a rate sufllcient to maintain a superficial oil velocityupward of about one foot a minute through 30 feet of one inch Raschigrings, the resultant desulphurization with 98% acid supplied throughspray l5 was as follows: Acid rate lbs./'bbl 10 20' 30 Final sulphur0.30 0.21 0.04

Under similar conditions when using 93% acid the following results wereobtained:

Acid rate lbs./bbl 0 I 20 '30 Final sulphur 0.33 9.22 0.06

Due to better treating 'control and prolonged surface contacting, themultiple tower system, as illustrated in Fig. 2, is preferred and moreemcient desulphurlzation is obtained. The following data was taken frommultiple tower operation on a similar raw stock of 0.70% sulphur,

The polymerization loss in the table above is based on the loss of theraw stock charge.

On examination of the above data a point of major significance is notedin that prolonged surface contacting results in a combination of sulphurremoval by selective sulphonation and polymerization and of the two thelatter factor is of major importance.

To illustrate further the action of the sludge and acid through themultiple tower system the curves of Fig. 3 are presented. Thedesulphurization efliciencyof the sludge under conditions of prolongedsurface contacting is apparent with maximum desulphurization by means ofselective polymerization.

This treating action results in the production of sludge spent to a muchgreater degree than in other known processes. The following data wastaken from commercial operation on high sulphur California pressuredistillates. Referring to Fig. 2, the acid sludge samples were takenbetween towers 33 and 32, 32 and 3|, and from of said unsaturates.

line 62 through which the sludge is withdrawn from the system, when the98% acid passes but once through the system.

on another occasion when treating a highly unsaturated stock DensityBaum H1804 at 60 F. grav. by wt.

Between towers 33 and 32 1. 260 29. 9 47. 4 Between towers 32 and 31 1.229 27.0 44. 8 Leaving line 62 to sludge tk. 75 l. 208 25.0 44. 8

and on a third occasion Density Baurr H2804 at 60 F. grav. by wt.

- Between towers 3s and s2 1. 312 34. 5 58.1 Between towers 32 and 31 1.183 22. 5 51. 1 Leaving line 62 to sludge tk. 75 1. 142 18. 46. 7

The Baum gravity of the sludge will vary during treatment within thefollowing limits.

Between towers 33 and 32 25 to 46 Between towers 32 and 31... 20 to 35Baun Leaving line 62 to sludge tk. 75 15 to 35 A regulation, ordampening eiTect, of the fresh acid on the oil is obtained by theregulated mixing .of acid sludge with the fresh acid. With moderncracking technique designed to obtain a relatively high percentage ofunsaturated hydrocarbons from petroleum for use in finished motor fuelof high anti-knock value, and as these hydrocarbons are readily attackedby sulphuric acid under various conditions, it is found that the mixingof portions of the acid sludge with the'fresh acid may be beneficial ineffecting selective sulphonation, and polymerization on sensitive stockswhereas fresh acid alone may cause an unnecessary sulphonation andpolymerization This is a special method for controlling the treatmentalthough not normally required on ordinary oil including Dressuredistillate stocks.

l-ieretofore, it has been proposed to modify the action of the sulphuricacid by dilution with water but it 'is found that much better operatingconditions result from dilution with acid sludge because of the peculiarproperties of the acid sludge consisting of reactive acid and acid de--riv'atives which are in themselves selective polyv merizers.

The function of the circulating pumps is merely that of circulating anddispersing while maintaining a temperature control in the treatingtowers. This is best accomplished in making a high ratio of oil to acid,or acid sludge, in the circulating pumps, so that the rise of.temperature through the pumps is a minimum. Furthermore, when on-streamflow is established, the supply of cooled oil, for instance to pump l8from tower I8, is such that with the high ratio of oil to acid used nocoolers are required immediately afterthe acid is injected between pumpl6 and tower i3 to maintain controlled temperatures throughout thetreating system.

With an entry temperature of 40 F. into tower l3 a similar tower exittemperature may be maintained. On certain stocks it may be desirable tocontrol the outlet temperature either higher or lower than the inletalthough normally a lower or like outlet temperature is preferred.

When fresh acid is injected into the suction of the circulating pump inthe novel method described. pump contacting or treating can be reducedto an absolute minimum and this way maximum film contacting in towersobtained. To illustrate this point data is shown for circulating ratesof /2 and to one on a treat of 20 pounds of acid per barrel of oil andwith 98% acid on California pressure distillate.

' Temp. F. Temp. F. BParrlgls Bl rgls gl gm ClIC a g circua ng chargedcirculated pump pump It has been found that under low circulating ratesof to one or less that overtreating occurs from the abnormal acidtreating rates on a small portion of the oil and desulphurization isonly obtained with excessive sulphonation and polymerization losses.circulating of 5 to 1 more or less the treating in the circulating pumpand connecting lines can be reduced to a minimum by the dilution effeetwhich is equivalent to feeding the fresh acid into the oil in smallincrements and the treating temperatures can be controlled by directcontact with the circulated oil. For example, on a 20# per barrel treatand a circulating rate of 5 to l the maximum acid rate to which the oilis subjected within the circulating pump system is 4 pounds per barrel.On the multiple tower system this same principle may be used incirculating oil between the towers.

The above method of controlled acid and acid sludge contacting incirculating pumps and connecting lines is a vast improvement over othermethods heretofore described and known in the art.

The following figures show desired ratios of oil to acid to minimizeacid reactions in the circulaing pumps and teach that there should neverbe an excess of acid or acid sludge in contact with the oil when sulphurremoval by selective sulphonation and polymerization is desired, asopposed to sulphur removal by greater solvent action of sulphuricacidwherein sulphonation and polymerization of valuable unsaturatedhydro- On the otherhand, with high carbons occurs to a larger extent.Theratios in this case will be given in terms of the oil charge to thetreating plant, 1. e., volume of oil circulated to volume of charge.These ratios may vary from A; to 1 or less, up to' 10 to 1 or more, de-

pending on conditions as characteristics of oil,

acid rate temperatures, etc.

The temperature rise through the circulating pump depends on the acidrate and rate of circulation. When speaking of pressure distillatecirculating ratios we mean the ratio of the pressure distillatecirculated to the pressure distillate charged. For example, if thecharge rate to the plant is 2500 barrels and the pressure distillatecirculating between two towers is 5000 barrels per day the pressuredistillate ratio is 2:1.

For low pressure distillate ratios, e. g. :1 or lower, the temperaturerise across the pump may reach 30-50 F. indicating a tremendous reactionacross the pump due to excessive acid and a longer agitating time. Whenthe circulation rates on the pressure distillate go up to 5:1 or higherthe temperature rise is reduced to 0-10 F. so that the amount ofreaction in the pumps is reduced to a minimum as indicated by the lowtemperature rise.

We prefer to circulate in ratios of about 2:1 for normal acid rates of10 pounds per barrel,

but depending 'on the stock being treated, the acid treat, etc., thecirculation rates may vary from 1:1 or less to 10:1 or more.

The invention comprehends the utilization of the acid sludge wheresoeverderived and in fact acid sludge from outside the system may be used.

To this end, the acid sludge from settling tower l8 may also be whollywithdrawn together with the required volume of preccoled oil and passedto pump l6. However, as the volume of sludge from tower I8 is oftennegligible, it may be advisable to pass the whole of it to the sludgetank 30. A sludge level M-M may therefore be permitted to form in towerl8 and a line 20a placed to withdraw the required amount of cooled oilfrom above such sludge level. Line 20b will then permit the addition tosuch cooled oil of a regulated volume of acid sludge for passage throughpump l6 back to tower IS.

A similar arrangement can be made with respect to multiple toweroperation shown inFig. 2 in which the sludge from tower 34 may be passedas a whole to pump 31 through line 35, or passed as a whole to sludgetank 15, or a sludge level M'M' may be maintained and regulated vol--umes of cooled oil and acid sludge may be withdrawn through lines 350.and b respectively.

Additional points of value in treating therefore comprise the supply ofacid or sludge in predetermined volume to the suction side of thecirculating pump together with an" established high ratio of oil whichavoids an excessive quantity of acid or acid sludge being present at anytime which might overtreat a portion of the oil with consequentexcessive temperature rise due to reaction at this point. At the sametime high oil to acid or acid sludge ratio and the agitating effect ofthe circulating pumps is valuable in 7 providing a means for dispersaland spraying of the acid particles to give a uniform distribution of theacid over the surface of the contact material in the towers.

Another valuable feature in mixing high ratios of oil to acid is tomaintain the fluidity of the acid or acid sludge for effective contactand flow in the treating towers. In general, the fluidity of acid sludgevaries with heat as shown.

In the following tabulation which illustrates the relative fluidities ofacid sludges produced at different treating temperatures, the sludgesresulted from the treatment of a California pressure distillate with 20pounds of 98% acid. per barrel. Viscosities were taken by means of afurol viscosimeter. l

Treating temperature 60 F. F. 20 F.

Viscosity at 100 F., furoi. 75 65 5B Viscosity at 40 F., iuroL. 800 500400 Viscosity at 0 F., lurol 5000 3500 2500 ent through each treatingtower.

The importance then of maintaining a temperature gradient through thetreating tower is apparent. A presure suflicient to maintain sulphurdioxide or other light vapors in solution or liquid phase is held on thesystem by suitable'back pressure I valves. The pressure is normallyabout 10 pounds per inch, depending on the treating temperature.However, at very low temperatures or with very light stocks a pressurehigher or lower than the above normal range may be required. tomaintainSCh or other vapors in solution and thereby decrease thevelocity through the towers.

In the multiple tower system another feature is I the maintaining ofgradually decreasing tempers atures through the system. On certainstocks it may be desirable, e. g.,- to treat the incoming oil with thespent sludge at -60 F. and then in subsequent towers decrease thetemperature to 30 F. or lower temperatures. This permits maximum filmcontacting between the sludge and oil and a spending of the sludge to aparticularly low acid content. It also enables lower temperatures to beused when the oil is approaching fresh acid treatment in the last tower.The process is ex-. tremely flexible in operation and the degree oftreatment can becontrolled through him and pump contacting by changes incirculating rates, temperatures, etc.

The use of higher temperatures when contacting the oil with sludge whichis approaching its the rerunning operation.

For example, when treating a pressure distillate of 400 F. end point (A.S. T.'M. distillation) the volume of bottoms which remit from thedistillation or rerun operation in which the overhead distillate is cutto the same volatility characteristics as the original raw oil, iscalled the polymerization loss. The percent polymerization loss is thevolume of bottoms divided by the volume of square inch to pounds persquare original raw oil charged to the acid treating unit times 100.

In general, the polymerization loss may be designated as follows:

Let A=the percent oil of desired volatility characteristics in theoriginal charge to the acid treating units.

Let B=the percent oil of similar volatility characteristics in the acidtreated oil.

The percent polymerization loss is then A-B =TX 100 Pressure distillateis a fraction of oil usually resulting from the pyrolytic decompositionof hydrocarbons during what is normally termed by those skilled in theart as the cracking process, but while the invention is particularlyapplicable to the treatment of pressure distillate, orcrackeddistillate, due to the refractory nature of its contained sulphurcompounds, the scope of invention is limited only by the terms of theappended claims.

We claim as our'invention:

1. The process of selectively polymerizing sulphur compounds inhydrocarbon oils, which comprises: flowing a stream of oil cooled to atem-' perature between 0 F. and 40 F. upwardly through a series oftreating towers containing contact material and simultaneously flowing astream of sulphuric acid sludge through said towers countercurrent tosaid oil stream and over said contact material, cooling the oilintermediate two towers in the series, and maintaining the inlet andoutlet temperatures of the oil from each tower substantially constant bypassing the acid sludge from the lower part of one tower to the upperpart of a succeeding tower in its direction of flow together with avolume of said cooled oil between about one-half to ten times the.volume of the initial oil stream.

2. The process of selectively polymerizing sulphur compounds inhydrocarbon oils, which comprises: flowing a stream of oil cooled to atemperature between 0 F. and 70 F. upwardly through a treating towercontaining contact material and simultaneously flowing a mixture offresh sulphuric acid and sulphuric acid sludge downwardly through saidcontact material, withdrawing said oil from the upper part of said towerand reducing the temperature thereof, withdrawing acid sludge from thelower part of said tower, passing at least a portion of said withdrawnacid sludge to mix with said fresh sulphuric acid, and passing saidmixture into the upper part of said tower together with a volume of saidwithdrawn oil between one-half and ten times the volume of the initialoil stream.

3. The process of selectively polymerizing sulphur compounds inhydrocarbon oils, which comprises: serially flowing a stream of oilcooled to a temperature between 0 F. and 70 F. upwardly through a seriesof treating towers, containing contact material and simultaneouslyflowing a stream of sulphuric acid and sulphuric acid sludge downwardlythrough said contact material in .a stream countercurrent to said oil,the upper part of the last tower in the series in the direction of theflow of the oil receiving fresh sulphuric acid, mixed with acid sludgederived from a preceding tower in said direction'of oil flow, togetherwith a volume of cooled oil derived from said last tower betweenone-half and ten times the volume of said initial oil stream.

4.1naprocess of reflninghydrocarbon oils with sulphuric acid in whichthe oil is cooledto a temperature between 0 F. and 70 F. and flowedupwardly through the units of a series of treating towers eachcontaining contact material to be taken from the upper part of apreceding tower in its direction of flow and passed to the lower partofa succeeding tower and having its temperature reduced intermediatesaid units while a stream of sulphuric acid with acid sludge is flowedthrough said units countercurrent to said oil stream and being passedfrom the lower part of one unit to the upper part of a succeeding unitin its direction of flow, the combination of steps which comprises:introducing fresh sulphuric acid into the upper part of the first unitof the series in the direction of flow of the acid together with avolume of said cooled oil between one-half to ten times the volume ofoil charged to said first unit and modifying the effect of the freshsulphuric acid on said oil by the addition thereto of acid sludgederived from a succeeding unit in such series in the direction of acidflow. 5. The process of selectively polymerizing sulphur compounds inhydrocarbon oils of the motor fuel type, which comprises: seriallyflowing a continuous stream of the oil upwardly through each of a seriesof treating towers each containing contact material, simultaneouslyflowing a stream of sulphuric acid sludge through said towerscountercurrent in each tower to said oil stream and over said contactmaterial by passing sulphuric acid of a concentration of from about upto including fuming acid into the upper part of the last tower in theseries and removing the same in its serial flow from the lower part ofeach tower to be injected into the upper part of a preceding tower inthe series, and effecting selective polymerization of the major portionof said sulphur compounds during contact of the oil and acid sludge bymaintaining a temperature between about 0 F. and F. in each tower andsuch time of contact of the oil and acid sludge therein that the gravityof the acid sludge finally removed from the first tower in the seriesfirst receiving said oil remains between about 15 to 35 degrees Baumwhen a cracked California distillate of about 59 degrees Baum isinitially contacted in said last tower with sulphuric acid of about 93%to 98% concentration; said temperature. being maintained by cooling theoil stream entering the towers from about 0 F. to 40 F. and passing withsaid injected acid sludge a volume of contacted oil between one-half andten times the volume of the initial oil stream.

6. The process of selectively polymerizing sul phur compounds inhydrocarbon oils, which comprises: flowing a stream of oil cooled to atemperature between 0 F. and 70 F. upwardly through a plurality oftreating towers containing contact material and simultaneously flowinga. stream of sulphuric acid sludge through said towers countercurrent tosaid oil stream and over said contact material, cooling the oilintermedi-.

ate two towers in the series, and maintaining the inlet and outlettemperatures of the oil from one tower substantially constant by passingthe acid sludge from the lower part of a preceding tower to the upperpart of said first mentioned tower in its direction of flow togetherwith a volume of said cooled oil between about one-half to ten times thevolume of the initial oil stream.

THOMAS OLIVER EDWARDS. JR. DAVID DEWEY STARK.

